Chapter 13: Meiosis Flashcards
Somatic Cells
All cells other than sex cells
Gametes
Sex cells ( sperm or egg)
Autosomes
The chromosomes which code for information other that gender (22 pairs)
Sex Chromosomes
The chromosomes which code for information including gender. The 23rd pair X or Y
Homologous Chromosomes
The pair of chromosomes which code for the same trait
Humans have a set of 23 homologous chromosomes
Karyotype
It identifies the number and types of chromosomes present in a species
Diploid
The have two Homo logs of each chromosome
They 2 alleles of each gene
Humans are this
A full set of chromosomes. A pair of each homologous chromosome
Haploid
They have only one of each type of chromosomes
They have just one allele of each gene
1/2 the number of chromosomes as a parent cell. 1 of each homologous pair.
What do each species have ?
Haploid number (n)
— indicates the number of distinct types of chromosomes present
—- Sex chromosomes count as a single type
—- In humans , n , is 23
What does the cell’s ploidy indicates? , 2n, n, 3n
The number of complete chromosomes set it contains
What do diploids cells have?
A paternal chromosome that came from the father
A maternal chromosome that came from the mother
Humans are diploids 2n = 46
Polyploid
Organisms w/ 3 or more versions of each type of chromosome , 3n 4n etc.
Tetraploidy, Hexaplod, Triploidy
Does having more chromosomes make the organism more complicated?
No, the # of chromosomes does not denote biological complexity
Meiosis v. Mitosis
Meiosis
-Occurs in 2 stages
- Begin with1 diploid cell & end with 4 haploid cells
-Gametes
Mitosis
-Occurs in 1 stage
-Begins w/ 1 diploid cell & end w/ 2 diploid cells
- Somatic Cells
Reductional Division
When the number of diploids is reduced to a haploid.
Result of Meiosis I: In 2 haploid daughter cells with replicated chromosomes
What happens during meiosis II ?
Sister chromatids separate.
What is the 1 division of meiosis?
Separation of homologous pairs
2n –> 1n
What is the 2nd division of meiosis?
Separation of sister chromatids
1n –> 1n
What is crossing over?
During Prophase I, homologous pairs swap pieces of chromosome, sister chromatids intertwine.
Random Fertilization
Any 2 parents will produce a zygote w/ over 70 trillion diploid combos
Sources of genetic variability
- independent assortment
homologous chromosomes in Meiosis I - crossing over
b/tw homologous chromosomes in prophase I - random fertilization
random ovum fertilized by a random sperm
Nondisjunction
the failure of the chromosomes to separate which produces daughter cells w/ abnormal numbers of chromosomes.
Trisomy 21
Down Syndrome
- delayed mental and social skills
- decreased muscle tone at birth
- asymmetrical or odd-shaped skull
- small skull
- small mouth w/ protruding tongue
- broad short hands
- increased risk of developing Leukemia and Alzheimer’s later in life.
